console.log(document.getElementById('sum').style)

function main() {
    let parent = document.getElementById('parent').value;
    let son = document.getElementById('son').value;
    let num = 0;
    while (parent.indexOf(son) != -1) {
        num++;
        parent = parent.slice(parent.indexOf(son) + 1, parent.length);
    }
    console.log(num);
    document.getElementById('sum').innerHTML = num;
}